Thirty-three children treated for congenital hyperinsulinism (CHI) (13 boys; 13 with focal forms of CHI, median age 10 months) entered the study. The mothers were requested to fill-in the Ages and Stages Questionnaire to estimate communication, gross motor, fine motor, problem solving and personal-social skills. Children with focal forms had significantly higher values on the ASQ Total, communication, fine motor and problem-solving scores. The probability of a child to be rated 'on schedule' in three and more developmental areas was significantly higher in the focal CHI group. The same was true for communication, fine motor and problem solving skills. Focal pancreatic resection was associated with higher chances of a child having 'on schedule' development in communication and problem-solving areas as opposed to no surgery. Children requiring medications after the surgery had lower chances to have appropriate development in communication and problem-solving areas.